A number of different applications of catadioptric imaging systems for far-field and near-field interferometric confocal and non-confocal microscopy have been described such as in commonly owned U.S. Pat. No. 6,552,852 (ZI-38) entitled “Catoptric And Catadioptric Imaging Systems” and U.S. Pat. No. 6,717,736 (ZI-43) entitled “Catoptric And Catadioptric Imaging Systems;” U.S. Provisional Patent Applications No. 60/447,254, filed Feb. 13, 2003, entitled “Transverse Differential Interferometric Confocal Microscopy,” (ZI-40); No. 60/448,360, filed Feb. 19, 2003, entitled “Longitudinal Differential Interferometric Confocal Microscopy for Surface Profiling,” (ZI-41); No. 60/448,250, filed Feb. 19, 2003, entitled “Method and Apparatus for Dark Field Interferometric Confocal Microscopy,” (ZI-42); No. 60/442,982, filed Jan. 28, 2003, entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter,” (ZI-45); No. 60/459,425, filed Apr. 1, 2003, entitled “Apparatus and Method for Joint Measurement Of Fields Of Scattered/Reflected Orthogonally Polarized Beams By An Object In Interferometry,” (ZI-50); No. 60/485,507, filed Jul. 7, 2003, entitled “Apparatus And Method For High Speed Scan For Sub-Wavelength Defects And Artifacts In Semiconductor Metrology,” (ZI-52); No. 60/485,255, filed Jul. 7, 2003, entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution,” (ZI-53); No. 60/501,666, filed Sep. 10, 2003, entitled “Catoptric And Catadioptric Imaging Systems With Adaptive Catoptric Surfaces,” (ZI-54); No. 60/602,046, filed Aug. 16, 2004, entitled “Apparatus And Method For Joint And Time Delayed Measurements Of Components Of Conjugated Quadratures Of Fields Of Reflected/Scattered Beams By An Object In Interferometry,” (ZI-57); and U.S. patent applications Ser. No. 10/778,371, filed Feb. 13, 2004, entitled “Transverse Differential Interferometric Confocal Microscopy,” (ZI-40); Ser. No. 10/782,057, filed Feb. 19, 2004, entitled “Longitudinal Differential Interferometric Confocal Microscopy for Surface Profiling,” (ZI-41); Ser. No. 10/782,058, filed Feb. 19, 2004, entitled “Method and Apparatus for Dark Field Interferometric Confocal Microscopy,” (ZI-42); Ser. No. 10/765,229, filed Jan. 27, 2004, entitled “Interferometric Confocal Microscopy Incorporating Pinhole Array Beam-Splitter,” (ZI-45); Ser. No. 10/816,180, filed Apr. 1, 2004, entitled “Apparatus and Method for Joint Measurement Of Fields Of Scattered/Reflected or Transmitted Orthogonally Polarized Beams By An Object In Interferometry,” (ZI-50); Ser. No. 10/886,010, filed Jul. 7, 2004, entitled “Apparatus And Method For High Speed Scan For Sub-Wavelength Defects And Artifacts In Semiconductor Metrology,” (ZI-52); Ser. No. 10/886,157, filed Jul. 7, 2004, entitled “Apparatus and Method for Ellipsometric Measurements with High Spatial Resolution,” (ZI-53); and No. t.b.d., filed Sep. 10, 2004, entitled “Catoptric And Catadioptric Imaging Systems With Adaptive Catoptric Surfaces,” (ZI-54). In addition, U.S. patent application Ser. No. (ZI-48) 10/218,201, entitled “Method for Constructing a Catadioptric Lens System,” filed Apr. 1, 2004 described one way to make some of these catadioptric lens systems. These patents, patent applications, and provisional patent applications are all by Henry A. Hill and the contents of each are incorporated herein in their entirety by reference.
In each of the applications of catadioptric imaging systems for each of the cited U.S. Patents, U.S. Patent Applications, and U.S. Provisional Patent Applications, a beam-splitter is incorporated in generating an image of an object with zero optical aberrations for a measurement object located on the optic axis of the imaging system. The beam-splitter is located at an interface between relatively thick optical elements of the catadioptric imaging systems. The optical elements contribute off-axis aberrations and cause a significant portion of optical paths in the catadioptric imaging systems to comprise a transmitting refractive medium such as fused silica or CaF2.
In each of the applications of catadioptric imaging systems for each of the cited U.S. Patents, U.S. Patent Applications, and U.S. Provisional Patent Applications, tight tolerances are generally placed on the manufacture of optical elements. In addition to the tolerances normally encountered in designing a diffraction limited imaging system, there are additional tolerances imposed in interferometric confocal and non-confocal microscopy applications. The additional tolerances are for example on surfaces of certain elements with respect to radii of curvature and on relative locations of centers of curvature of the surfaces of the certain elements.
The additional tolerances lead to improved performance of a catoptric or a catadioptric imaging system, e.g., with respect to increasing the average intensity of desired images by a factor of approximately 2 and reduced intensity of spurious beams by one or more order of magnitudes, and in addition make it possible to realize interferometric reduction of background fields. The interferometric reduction of background fields leads to a reduction of statistical errors. The increase in intensity of desired images and the reduction of statistical errors lead to an increase in signal-to-noise ratios and to a concomitant increase in throughput of a metrology tool using the catoptric or catadioptric imaging system. The interferometric reduction of background fields further leads to a reduction of systematic errors. A consequence of the reduction of systematic errors is a reduction of the computational task required to invert arrays of measured interference signal values to a multi-dimensional image of a measurement object.
The cited U.S. Patents, U.S. Patent Applications, and U.S. Provisional Patent Applications further teach the use of adaptive catoptric surfaces in a catoptric or catadioptric imaging system. The use of adaptive catoptric surfaces in a catoptric or catadioptric imaging system makes it possible to relax tolerances on the surface figures of elements, to relax tolerances on locations of surfaces of the elements in the catoptric or catadioptric imaging system, and to compensate for certain optical aberrations such as may be introduced by the pellicle or aperture-array beam-splitter. The factor by which the tolerances may be relaxed on the surface figures is of the order of 5 for certain of the elements. The use of adaptive catoptric surfaces in a catoptric or catadioptric imaging system further makes it possible to introduce a vertical or lateral scan of a measurement object or substrate being imaged at slew rates higher than possible and/or practical when the vertical or lateral scan must otherwise be introduced either by translations of an entire catoptric or catadioptric imaging system and associated optics and detector systems or translations of the measurement object or substrate, e.g., a 300 mm wafer, and the measurement object or substrate support system.
The cited U.S. Patents, U.S. Patent Applications, and U.S. Provisional Patent Applications further teach the replacement of a beam combining beam-splitter in an interferometric imaging system with a thin fluorescent layer or interface.
The cited U.S. Patents, U.S. Patent Applications, and U.S. Provisional Patent Applications also teach the use of an N-dimensional bi- and quad-homodyne detection methods.